On Mon 19-03-18 16:29:30, Li RongQing wrote: > mem_cgroup_force_empty() tries to free only 32 (SWAP_CLUSTER_MAX) pages > on each iteration, if a memory cgroup has lots of page cache, it will > take many iterations to empty all page cache, so increase the reclaimed > number per iteration to speed it up. same as in mem_cgroup_resize_limit() > > a simple test show: > > $dd if=aaa of=bbb bs=1k count=3886080 > $rm -f bbb > $time echo 100000000 >/cgroup/memory/test/memory.limit_in_bytes > > Before: 0m0.252s ===> after: 0m0.178s One more note. I have only now realized that increasing the patch size might have another negative side effect. Memcg reclaim bails out early when the required target has been reclaimed and so we might skip memcgs in the hierarchy and could end up hamering one child in the hierarchy much more than others. Our current code is not ideal and we workaround this by a smaller target and caching the last reclaimed memcg so the imbalance is not so visible at least. This is not something that couldn't be fixed and maybe 1M chunk would be acceptable as well. I dunno. Let's focus on the main bottleneck first before we start doing these changes though. -- Michal Hocko SUSE Labs
